Flooring options and structural support minimums?

[LDavis]

Rob, I'm moving this from the "advice" board so I can "split hairs". Hardibacker's minimum requirements for plywood are 5/8 EG. If there is 3/4 under the particle board, she actually exceeds plywood minimums. (Assuming EG and deflection within acceptable limits).

In theory, I share Keith's tendency toward "over-kill" and always try to "sell" an installation in excess of minimum requirements.

In reality, I'm lucky to sell/justify minimums too much of the time. I passed on a job about 1 1/2 years ago where the home owner wanted me to install apprx. 500 sf of ceramic directly over OSB. I told them I'd be interested in doing the job, but they would have to allow me to include hardibacker and some waterproofing (attached wet-bath) in the bid. No dice! I "walked" thinking "I'll get the demolition and re-do down the road".

About 7 months ago I got the call. I did not recognize the name or address, but recognized the house when I arrived. The house had been sold (by owner) and the "new" owners wanted to know if I could "fix" their ceramic tile. To make a long story short, the new home owners are "mired" in the legal process of trying to recover damages to replace this mess. ("tile setter" has disappeared and original homeowners are claiming ignorance) No, I'm not getting in the middle of this one now!

I guess my rambling point is this, if I can at least meet minimums, then I've got the manufacturer involved in worst case scenario's, assuming I've met manufacterer minimums. (I bend over backwards to at least accomplish that)

All that said, I've got a question for the other forum "wizards" with respect to this L/360 and L/720 deflection minimums we hear so much about. I know what it means. What I don't know is how to measure this "gremlin" in a consistent, accurate, reproducable, meaningful manner.
Honestly, do any of you have a "device" that you use on EACH AND EVERY JOB WHERE DEFLECTION is a potential concern and is it accurate/reliable enough that your convinced an "impartial" inspector would reproduce your results in a worst case scenario?

Next question, what are the support standards ( 2x6, 2x8, 2x10, 2x12, engineered I-beam, steel I-beam, etc) and in combination with what dimension of plywood, OSB, etc, and over what spans to produce the desired deflection standards?
And if the proper dimension subfloor is installed over the proper dimension support, over the proper dimension span, does that then imply/support meeting one or both of the "deflection gremlins"?

I've been doing this type of job for awhile now and walking, jumping, inspecting, securing, recommending better than minimum installation standards seems to be working. But, if "push comes to shove" in a "legal" sense, how do I "PROVE" the deflection standards are met?

HELP ME fellow setters, this one bugs me abit!

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[Dave Ashton]

L:

I dont know anyone who actually measures deflection on a job.

The amount a floor will deflect is really just a calculated number based on an assumed load (live and dead load combined) or one specified by the building code that is followed in your area. The calculated number is the maximum deflection a floor will experience when subjected to the load and this is compared to your allowable....L/360, L/720 etc. The L is the length of the span in inches. In the simplest of cases, the span is a "simple span", one supported on each end, and the maximum deflection will occur either at mid-span or at the point of maximum load.

So, what does all this jibberish tell you so far...not much probably. If you want to check to see if your floor complies with the deflection criteria..and by the way, deflection is the governing factor most of the time in residential construction, not strength, you can use the span tables for deflection in the building code. Figure out what your joist size and spacing is, measure the longest span, then look this up in the span table and see if it less than or equal to the maximum span for your load and deflection requirements. If it is, your OK, if not, you have to make a judgement call. Try and explain to the owner that the floor doesnt cut it, needs to be beefed up, and its going to cost them. Tile it anyway. Walk away.

The judgement call is where it gets tricky because remember the load is an assumed load. Residential floors need to be able to support 40 psf PLUS the dead load. Obviously tile and backerboard or tile and mud weighs more than carpet thus the dead load will be greater, the overall assumed load will be greater, and it will take a shorter span or a bigger joist, or joists spaced closer together, to limit the deflection. Does a residential floor ever see 40psf...probably not often, but the day the owner has a big party and it does, is not the day you want your grout or tile to crack...who did you say installed your tile??



Hope this wasnt too long or totally confusing,

Dave

PS..to answer one of your questions...if you are doing new construction, the floor should already meet the deflection criteria for all residential construction of L/360, so you should be covered as long as it passed the framing inspection. Assuming of course that the designer new the area was going to be tiled in the first place. The only(?)place you might run into trouble is natural stone which requires L/720. I would talk to the GC about that, more often than not it hasnt been taken into consideration. If so, you get to try and do a little education...or some CYA for later on.

[Edited by on 08-25-2001 at 06:24 PM]

[LDavis]

Dave,

I appreciate the response and no its not confusing, as a matter of fact it answers some important questions for me. Since I'm on the "finish" end of the business rather than the construction end, I was not familiar with the span tables for deflection you mentioned. Certainly makes sense though. But then you had to go and "muddy" the water with this "assumed load" and "40psf PLUS dead load". Ignorance WAS bliss, now I've got something else to worry about.

In your "PS" to Dave, you mention deflection criteria for all resdential construction being L/360. That made me feel better, but once again this is based on "assumed load". I wonder if the designers are as prone to "overkill" as some of us on the "finish" end. Your right, CBU, tile, thinset, mudbeds all weigh considerably more than Carpet/pad, vinyl, wood, etc. I've never been in the position to concern myself with the L/720 requirement for natural stone installations. I will only install natural stone on concrete slab or mud over slab.

Overall, you've steered me in the right direction and answered more questions than created. This "40psf plus" business is one of those things I'll need a mental picture of to fully comprehend. (Like....would that be the equivalent of of full grown elephant balancing on one foot in the middle of the floor span ....or something less?)

Thanks again Dave.

[cx]

Well, LD, that would kinda depend upon the size of your elephant and the actual span, wouldn't it?

For serious, when I have to order engineered floor systems, we always go for L/480 as a minimum and frequently buffer that a good bit. L/360 on a 16 foot span allows you more than a half inch and that just doesn't feel right to me, even if it is in spec. L/480 isn't really that much less deflection, but I swear I can tell the difference and it just doesn't cost enough more to even consider minimums on a new-construction custom.

Only time I've ever actually measured the deflection was on the house in the photos posted here. That 300 gallon tub was hung between two gluelam beams spanning 30 feet. The truss company was told what I was going to do and we threw in a good pinch of overkill. Still, before tiling that tub and laying the hardwood, I wanted to know exactly how much deflection we were dealing with.

Measuring method was simple: Set post under the beam with a dial indicator on top and zeroed it with the tub empty. Filled the tub and checked the guage. Got 1/8 inch deflection. Called it good. (Must admit I'd never even heard of L/360 back then (blush) but knew what I could live with).

Pretty gross overkill, perhaps, but it made the exposed beam size right asthetically too.

I like overkill. Nobody ever calls me back requesting that I cut a little off the floor joists to give'm a little bounce.

[LDavis]

CX,

Thanks for the input. I like your approach and propensity for "overkill". Its safe to say your probably the exception rather than the rule, at least in most of my recent experience with some of the "local yokels". Your experience with the "indoor pool" and measuring for deflection from below seems like the easiest, accurate, and most practicle approach possible. Got a good mental picture of this one! Thanks.

[Rob Z]

Hi Latney, Dave, and Kelly

I have seen similar set ups like Kelly referred to with the dial indicator gizmo. Do I ever fool with that sort of thing? No. I figure if there is ever a problem I'm screwed cos the MFR's warranties and their lawyers will somehow be such a pain in the ass that I'll give up. If anything happens more than that, then I'll be thrilled.


I don't remember ever setting tile over backer board on floors with just the MFR minimum underlayment. I think I've always added extra plywood. I figure it into the job, and I feel good about what the customer is getting.

There have been quite a few jobs where I was the high bidder since I included a hell of a lot more than the other guys, and didn't get the job. I got down in the dumps and cussed the butchers and the hacks out there, got upset with myself for not being a better salesman, and so forth. But always within days, I had better jobs with better customers so everything was okay.

As for the lady we were helping over on the other board...my main concern was trying to talk her out of leaving the particle board in place and skipping the thinset underneath. I do try to make it clear in my posts to the DIY'ers that some of the stuff I'm recommending is above and beyond the industry minimums. I also try not to get too carried away with selling a gold plated job to someone that will be taking on setting tile for the first time.


My main assignment from John is to keep things from getting carried away and overwhelming our DIY'er friends with too much advice.

I think we should keep on doing it the way we have been, being careful to emphasize to the beginners that we are explaining a way that has worked for us, not necessarily the only right way to do something.

That's my main beef with some of the other boards out there-too many people getting really nasty if someone has a different method from their Gospel.

Rob

[cx]

Latney:
When I bought my first dial indicator (back in an old aircraft repair life) they cost about the same as a medium wet-saw today, adjusted for inflation, of course.

But now you can get a pretty good one with an adjustable magnetic base for 50 bucks or so, I think. And it's probably as accurate, possibly more so. Definately close enough for what we're talking about.

Good for checking run-out on your saw blades, your disk brake rotors, and all sorts of other stuff - if you require justification for buying tools.

[cx]

Latney (continued):

Or you can borrow mine. I can drop it off where your spouse works on the way to the post office any day.

[John Bridge]

Guess I'm stuck with the "jump test."

Except in a few remodeling jobs, I never have to worry about deflection. I'm either on a concrete slab, or I'm over trusses with 1 in. t&g ply.

Of course, I have to worry about slabs cracking . . .

[LDavis]

CX,

If its $50 or less, it will probably end up somewhere on my truck. I,m a "toolaholic". Anything that makes the job easier, faster, more productive, accurate, or just "looks purty" stands a very good chance of finding its way to my arsenal.

Rob,

I think you do an excellent job as the "advice" moderator. As a collective, this group can/will overwhelm all who dare enter the door. (I'm overwhelmed most of the time) I constantly learn something new here. Don't always agree 100%, but always learn. Different methods/opinions keeps me on my toes examining why I do what I do, and should/could I be doing something different.

John,

I'm still partial to the "jump test" myself. I think Rob's probably right, the manufacterer's have the "legal/financial" deep pockets to shift/place, as the case may be, the "warranty criteria met" standard as needed.

(Art, this is not an "assault" on you or any one specific. We could not do the job without the products. But the "frontline" is routinely decimated in "legal assaults". And rightly so in many cases where manufacturing instructions are not adhered to!)

[Rob Z]

Latney

Thanks...put in a good word to John for me please. I'm due for a raise soon. Keep on disagreeing. None of us has a lock on the Truth.

Kelly

Do you have a source for one of those indicators? I asked a machinist I know, and he got all excited and started showing me the stuff he uses to build parts for the space shuttle, and it's too expensive.

A $50 tool is well below the threshold where I have to have a debate with the tool committee at RZ Remodeling.

[John Bridge]

Yeah, fifty bucks can be chalked up to "expendables." Patti is our bookkeeper, and I have to account to her after every job. I can charge "expendables" once every week or two. [Of course, then it comes out of my gas money.]

[John Bridge]

Before we get too far off track here, somebody explain to me the thinking behind this 19 point something joist spacing I keep hearing about.

[LDavis]

John,

I believe the 19.2" oc joist spacing is in reference to the "engineered" wood I-beams/floor trusses. I'm not certain, but I think the only TCA recommendation here mandates use of an "uncoupling" system in this application.
(Can't find my TCA handbook, someone correct me if I'm wrong...like I had to ask!)

[kalford]

Art???????????

[Bud Cline]

John,

19.2" spacing is a money saving meneuver I think. Not as good as 16"oc, but better than 24"oc.

An 8 foot span 16"oc requires 7 members
where an 8 foot span 19.2"oc requires only 6 members.

An 8 foot span 24"oc requires only 5 members but we all know what that does to a tile guy.

I think your right tho this all probably began with I-Joists.

[cx]

Jana's Daddy:

After much brain racking (wraking?), I can't recall where I got the last dial indicator. It is a YUASA, by brand name, an appellation otherwise foreign to moi.

I know WW Grainger will have some, but not at the best prices. We have a humongous catalog from MSC Industrial Supply that has a couple dozen choices ranging from about $60 to some hundreds of dollars. They have a web site, but you have to look through the pages with that acrobat thingee which usually makes me wanna just take the beatin'.

I'm thinking I didn't mail-order the last one, but.........

Not sure your local chepo auto parts store might not be the place. I'll keep thinking - well, my version of it anyway.

And I can't help adding: At Kelly's Custom Homes the tool purchasing committee is always in agreement with my recommendations. Bit of a benevolent dictatorship actually. The voting goes quickly and is always unanimous.

[Dave Ashton]

Hey guys,

Before I forget....Rob is so dedicated to his work that he even wears his Red Wings to the beach!

Having an engineering background this deflection stuff is somewhat fun for me so Im going to add some more junk.

Lets all remember that whatever is specified in the UBC is the minimum standard. (And we all know that some builders do fail to even meet these minimums. The old military evaluation report...fails to meet the low standards he sets for himself...) Also remember that residential construction is governed more by deflection than by strength of an induvidual member. Thats why the jump test works because if it moves "uncomfortably" when you give the old jump at mid-span, it might be too bouncy for tile. (Especially if Rob and Bud drink a few too many and decide to have a WWF championship match...but, that would probably be at one of our houses so we'd be safe...anyway, tangent) Back to live and dead loads

Residential live load....a bunch of people at your house milling around admiring your excellent tile job. Usually 40psf. This is 40 pounds per square foot over the whole floor and each component of the floor supports a portion of the 40. Make any more sense? Its kind of a hard concept to grasp mentally, at least it was for me.

Dead Load. This is the weight of the building materials all added up and expressed as a psf load. Joists, subfloor, mortar bed, tile, etc. Furniture and that kind of stuff is included in the live load, except for big stuff like baby grand pianos or Robs beer fridge...those are special case kind of things. This gets added to the dead load to get what we'll call the design load.

So, the highly trained architect(anyone laughing?) that designed(how about now?) the house added this all up took it into consideration when sizing the joists and spans and you have nothing to worry about.

Dave

[Rob Z]

FYI Dave

Most of that week was bare feet or flip flops, but the trek through the briars there required some boots for me.

If any of you are ever in Nags Head, check out "Tortuga's Lie". We went there almost every night for dinner. Excellant seafood, and the only place on the planet that doesn't consider Bass and Guinness as premium beers.

[chip]

Man, I gotta get into this tile setting thingy.

I can't even afford to go to Miami, and it's 30 miles away.

Latney, or was it Keith? I can't remember and I'm not going back through all of that to find out. I have never walked on to a job complaint and found one installer who hadn't followed the instructions on the bag. I mean every time I go on the job site, tile installers are sitting around reading thin set and or grout bags!! It's amazing!!!

No seriously, I know where you are coming from and it is tough on everyone. The bad rap on the manufacturers comes from all of the failures out there where they didn't accept responsibillity. Were they always right? I doubt it, but you are all aware of the shoddy work that is being done out there and you are losing bids due to these "Tile Mechanics"?

There is no easy answer, but I will tell you this. The people who frequent this forum are the future of this "Industry". People who care about their craft and about the customer and what is good for all of us.

It's a pleasure to read and learn along with you guys and gals. Oh, yeah! You too Bud!!!!


Art